Increased mobile data usage and expected future mobile data usage and applications have been anticipated by various organizations such as the Third Generation Partnership Project (3GPP) and its Long Term Evolution (LTE) efforts. According to Release 8 of the Evolved UMTS Evolved Terrestrial Radio Access (“E-UTRA”) standard, downlink communications from a base station (also referred to as a base transceiver station (BTS) or an “enhanced Node-B” (eNB)) to a wireless communication device (e.g. a mobile station or also referred to as “user equipment” or “UE”) utilize orthogonal frequency division multiplexing (OFDM). The OFDM orthogonal subcarriers, used for communication with a UE, may be contiguous or noncontiguous and the downlink data modulation may be performed using Quadrature Amplitude Modulation (QAM), Quadrature Phase Shift-Keying (QPSK), 16-ary QAM (16QAM), or 64QAM. In contrast to the downlink, uplink communication from the UE to the eNB utilizes Single-Carrier Frequency Division Multiple Access (SC-FDMA) according to the E-UTRA standard. In SC-FDMA, block transmission of QAM data symbols is performed by first discrete Fourier transform (DFT)-spreading (or precoding) followed by subcarrier mapping to a conventional OFDM modulator. The data transmission from the mobile station or UE in the uplink is controlled by the eNB, and involves transmission of scheduling requests (and scheduling information) sent to the UE via downlink control channels. Scheduling grants for uplink transmissions are provided by the eNB on the downlink and include, among other things, a resource allocation (e.g., a resource block size per one millisecond (ms) interval) and an identification of the modulation to be used for the uplink transmissions. With the addition of higher-order modulation and adaptive modulation and coding (AMC), large spectral efficiency is possible by scheduling users with favorable channel conditions.
E-UTRA systems also facilitate the use of multiple input and multiple output (MIMO) antenna systems on the downlink. For example, MIMO antenna systems may be employed at the eNB through use of multiple transmit antennas and at the UE through use of multiple receive antennas. Such multiple antenna systems and MIMO operation may enhance either the UE's data throughput (single user MIMO) or the base station's data throughput (multi-user MIMO) if the base station employs multiple antennas. In such cases, UEs may share resources which provides even further spectral efficiency.
An eNB transmits a pilot or reference symbol and a UE, within the eNB's radio coverage area, may receive and use this information for channel estimation, subsequent data demodulation, and as a link quality measurement reference for reporting parameters related to the UE's radio reception. The link quality measurements, which are provided from a UE for feedback, may include spatial parameters such as rank indicator, or the number of data streams sent on the same resources; precoding matrix index (PMI); and coding parameters, such as a modulation and coding scheme (MCS) or a channel quality indicator (CQI). For example, if a UE determines that the link can support a rank greater than one, it may report multiple CQI values (e.g., two CQI values when rank=2). The reports may include wideband or sub-band frequency selective information of the parameters. The eNB may use the rank information, the CQI, and other parameters, such as uplink quality information, to serve the UE on the uplink and downlink channels.
In accordance with the E-UTRA standard, to send downlink data to the UE (or request uplink data from the UE), the eNB transmits a scheduling message (e.g., a scheduling grant message) via downlink control information (DCI) on a downlink control channel (e.g., a physical downlink control channel (PDCCH)) providing parameters for the desired data transmission scheme. The UL grant contains parameters provided by the eNB for use in generating the uplink subframe, including transport block size, data modulation and coding scheme, hybrid automatic repeat request (HARQ) information such as Redundancy Version (RV), resource allocation (e.g., resource blocks and position within overall system bandwidth), power control information, and other control information. Similarly, the DL assignments contain parameters provided by the eNB used in decoding the downlink subframe including transport block size, data modulation and coding scheme, resource allocation (e.g., resource blocks and position within overall system bandwidth), HARQ information, precoding matrix information, and other control information. The UL grants and DL assignments are typically transmitted over the PDCCH.
The OFDM downlink provides a subcarrier spacing of 15 kHz and a maximum of approximately 1320 subcarriers. Of course, the number of subcarriers available to a network operator depends on their available system bandwidth, that is, from 1.4 MHz to 20 MHz channel bandwidths. The control channel, i.e., PDCCH, transmissions consists of typically 1˜3 OFDM symbols at the beginning of each 1-ms sub-frame. Typically an OFDM symbol comprises of an integer number of time units (or samples), where a time unit denotes a fundamental reference time duration. For example, in LTE, the time unit corresponds to 1/(15000×2048) seconds. Thus, the PDCCH transmissions are a first control region with a fixed starting location (temporaneously) at the first OFDM symbol in a sub-frame. All the remaining symbols in a sub-frame after the PDCCH are typically for data-carrying traffic, i.e., PDSCH, assigned in multiples of Resource Blocks (RBs). Typically, an RB comprises of a set of subcarriers and a set of OFDM symbols. The smallest resource unit for transmissions is denoted a resource element which is given by the smallest time-frequency resource unit (one subcarrier by one OFDM symbol). For example, an RB may contain 12 subcarriers (with a subcarrier separation of 15 kHz) with 14 OFDM symbols with some subcarriers being assigned as pilot symbols, etc. Typically, the 1 ms sub-frame is divided into two slots, each of 0.5 ms. The RB is sometimes defined in terms of slot rather than sub-frame. Some RBs may be shortened or punctured to accommodate other information such as control information, synchronization signals, reference signals or pilots, sounding signals, etc.
The eNB providing the downlink transmits a subframe of 1 ms that is divided into two slots, each of 0.5 ms duration, with a Radio Frame defined as comprising ten subframes. The time-frequency resources or RBs in a subframe, which provide radio channelization, are allocated to the UEs. Further, the base station may use various modulation and coding schemes (MCS) and transport block sizes. A transport block size is the block size of the data or the number of information data bits being communicated, and this is typically the block received at the Physical layer from the MAC layer. Various modulation formats are accomodated on the downlink channels including QPSK, 16QAM and 64QAM.
In any case, such radio communication systems having allocated resources, including systems employing shared resources, may utilize various modulation and coding schemes for optimal bandwidth utilization and for optimum use of the resources for specific applications. Modulation and coding schemes may also be selected based on perceived radio propagation or noise conditions as determined by various network or user equipment (UE) based measurements. The UE must be provided with its TBS and MCS which requires signaling overhead and consumes bandwidth that otherwise could be used for data transmission.
Therefore a need exists for methods and apparatuses for determining an allocated Transport Block Size (TBS) and MCS by a UE in an efficient manner and with reduced signaling overhead.